Electrical Wiring - Greenheck MSX Installation, Operation And Maintenance Manual

Installation of Electric Heater
(optional)
WARNING
Electrical Shock Hazard! Disconnect all power
sources before doing any work on the unit.
General:
The requirements and practices described below
are based on the National Electric Code (NEC) and
The Space Heating Standard of the Underwriters
Laboratories Inc. (UL). Although UL requirements
are uniform throughout the country, local electrical
codes may deviate from the National Electrical Code.
Therefore, local inspection authorities should be
consulted regarding local requirements.
Electrical Wiring Instructions:
1. Use the wiring diagram supplied with the heater
as a guide in correlating field wiring with the
heater internal wiring.
2. All field wiring to the heater must meet the
requirements of the National Electric Code and
any other applicable local or state codes.
3. Wiring to the heater must be rated for 75°C
(167°F) minimum.
4. The fan is interlocked by the factory to the
control circuit so the electric heater will not
operate unless the fan is on.
5. If heater does not have a built-in disconnect
switch or main circuit breaker, install a remote
disconnect (furnished by others) in accordance
with the National Electric Code, Article 424-65.
Calculation of Line Currents (amps):
Single Phase Current =
EXAMPLE: 5 kW, 208 volt
5000 watts
= 24 amps
208 volts
Three Phase Current =
EXAMPLE: 14.4 kW, 208 volt
14400 watts 14400
=
208 volts x 1.73 360
®
watts
volts
watts
volts x 1.73
= 40 amps
Sizing of Supply Conductors
The required minimum size of supply conductors
is marked at the field wiring terminals within the
heater control box or reference the Supply Wire Size
table included in this section. The wire gauges are
calculated for 125% of the heater line current as
required by the National Electric Code, Article 424-3(b)
based on conductor insulation rated for 75°C (167°F).
Supply Wire Size
(Not more than six conductors in Single Conduit
Max. Heater
AWG or
Line Current
MCM
3
Copper
14 12
12 16
10 24
8 36
6 52
4 68
3 80
2 92
1 104
0 120
00 140
000 160
1
For 7-24 conductors in raceway or cable, reduce allowable
heater line currents to 87½% of those shown above.
2
Based on 30°C. (86°F.) ambient temperature, for higher
ambient temperature see National Electric Code table
310-16 and 310-18 Note 13.
3
Based on 80% of ratings in the National Electric Code
table 310-16 for 75°C insulation.
Effect of Low Voltage on Wattage and
British Thermal Unit (BTU)
The heating elements may be used on voltages
lower than the design voltage of the heater, however,
the wattage and BTU output will be reduced to the
percentages listed in the table below.
De-rated Wattage For Low Voltage
% of
Heater Line Heater
Voltage Voltage Wattage
and BTU
480 460 92
440 84
277 265 92
254 84
240 230 92
220 84
208 75
200 69
Max. Heater
AWG or
2
Line Current
MCM
Copper
0000 184
250 204
300 228
350 248
400 268
500 304
600 336
700 368
750 380
800 392
900 416
1000 436
% of
Heater Line Heater
Voltage Voltage Wattage
and BTU
208 200 92
190 83
120 115 92
110 84
Model MSX Make-Up Air
1
)
2
3
9